Conventional paperboard cartons for liquid food products are commonly constructed from paperboard sheets coated with a film of a heat sealable, waterproof thermoplastic material such as polyethylene, polyvinyl chloride or polypropylene. When heated, this plastic film becomes tacky, so that sheets thus coated and heated can be sealed together by being squeezed tightly together. The coated sheets are initially cut into flat carton blanks. These blanks are subsequently folded into a generally rectangular open-ended configuration, then are closed at one end by forming a bottom end wall via folding and sealing bottom end closure panels which extend integrally from the four side walls of the carton blank. The cartons can then be filled and sealed with a gabled or flat-folded top.
In a type of apparatus commonly employed for assembling paperboard cartons, the partially assembled, rectangular, open-ended cartons are individually loaded, top end first, onto a rotatable assembly having a number  of mandrels directed radially outward so that the bottom end closure panels extend beyond the end of the mandrels and describe a circular path as the mandrel rotates about a central axis. Along this circular path are a series of regularly spaced carton processing stations; as each rotating mandrel brings its respective carton bottom end into alignment with a processing station, the rotation stops momentarily so that the carton at each station can be processed appropriately. This indexing sequence allows for rapid processing of many cartons.
In addition to the infeeding station for loading the carton blanks onto the mandrel, other processing stations generally include heating, folding, sealing, cooling and outfeeding. The heating step can be performed before or after the folding step, as long as the plastic film coating remains sufficiently hot and tacky to form a strong bond at the sealing station. The present invention concerns the sequence of operation wherein the bottom end closure panels are heated prior to folding, as this is simpler in operation and minimizes movement of the carton after folding, thus resulting in improved bottom alignment, i.e., bottom square is improved.
Accordingly, each rectangular carton blank is loaded onto a mandrel, indexed to the heating station where the bottom end closure panels are heated, then is indexed again to a bottom panel folding station.
At the bottom folding station, as shown in FIG. 1, representative of known designs, the bottom end panels are folded inward and down to form the bottom end wall. The standard carton design as shown comprises a rectangular carton blank having open top and bottom ends, first, second, third and fourth body panels adjoining first, second, third and fourth bottom end closure panels, respectively, with the first and third bottom end panels oppositely disposed and scored to fold inwardly when the second and fourth bottom end closure panels are folded inwardly down to form the bottom of the carton. In practice, the carton blank is loaded onto the mandrel with either the second or fourth (unscored) bottom end panel facing in the direction of movement of the mandrel. At the folding station, a pair of break fingers contact and push inward on the first and third bottom end panels from the sides, which starts the actual folding of the bottom panels. This folding, or “breaking” of the scored bottom end panels acts to partially pull down the second and fourth bottom end panels, which are then biased further downward by a hooder assembly having a pair of inwardly angled surfaces. The hooder assembly moves up and down in line with the longitudinal axis of the carton, and the angled surfaces act to urge the second and fourth bottom end panels downward to substantially complete folding of the bottom end wall. 
This design, however, requires that the carton blank be loaded onto the mandrel with the two scored bottom end panels on the sides of the mandrel, relative to movement, so that the break fingers do not interfere with the carton rotation between stations. This can problematic for certain carton designs for which it is preferred that the carton assume a position 90° offset from standard. Such  carton designs thus require an extra turning step when utilizing known machinery.
After the bottom panels have been folded, further indexing of the mandrel advances the carton blank to the sealing station where the heated, folded bottom panels are sealed together to form the bottom end wall of the carton. In order to seal the folded end panels together, they are fused together by a bottom sealing plate which applies pressure to the folded end panels by pressing them between the sealing plate and the end of the mandrel upon which the carton blank resides.
Further indexing of the mandrel from the sealing station moves the carton blank to an optional cooling station, followed by a final indexing to an outfeed station, where the closed-end carton is set down on the now sealed flat bottom for filling and top sealing.